1. Field of the Invention
The present invention deals with a new type of wrapped thread and a process for its manufacture.
2. Description of the Prior Art
It is well known how to wrap threads. Schematically, this process consists of spirally winding a thread, called "covering" or "wrapping thread," around a second thread called "core thread." Depending on whether or not only one or several wrapping threads are used, it is described as a simple or a crossed wrapping. This technique of wrapping is very widely used in the fabrication of fancy threads and of elastic threads with an elastomeric core.
It is also known to use fragile threads, such as glass thread, threads of thermostable synthetic materials such as those made of aromatic polyamide, or threads of a refractory substance, with a cross directional sense of wrapping. In this case, the fragile thread forms the core, and the wrapping thread, advantageously made of synthetic thermoplastic material, is wound in a simple spiral (simple wrapping) in regular single and joined turns around the thread of the core which is kept in the shape of a straight line, whereby the wrapping thread protects the said core thread. Such a wrapped thread is described in the commonly assigned French Pat. No. 2,314,958, and it is used in the production of materials destined to reinforce plastic substances.
This latter technique, notably commercialized by L. Payen & Cie, still shows a certain number of inconveniences. Indeed, if, as is often the case, the core thread has a diameter which is greater than the diameter of the wrapping thread, the latter has the troublesome tendency to slip over the mentioned core. Therefore, the core thread is at once badly protected against abrasion from the outside, which means the abrasion suffered by the core thread with respect to another element, and equally badly against inside abrasion, which means the abrasion which is derived fromm the rubbings among the elemental fibers which form the core thread.
The present invention reduces these inconveniences. It deals with a new type of wrapped thread which has a very good resistance against abrasion from the outside as well as inside, and wherein the distinctive features of the core are practically unchanged by the presence of the thread of the outside wrapping.
Certainly, it is already known to make use of the phenomenon of gluing to modify the properties of thread-like textile elements. Thus, German Pat. No. DE-A 2,704,836 describes stringings, especially for supporting goods (tennis rackets) or musical instruments, where a core is covered by a binding liquid substance which dries immediately. Eventually, the core is covered by winding loose threads around it.
Moreover, it has been disclosed in the U.S. Pat. No. 3,644,866 to keep the parallel thread in position by means of a double-wrapped thread made in a loose manner. Before the wrapping, the core threads are bathed in a binding substance which ties them together.
The U.S. Pat. Nos. 2,313,058 and 2,424,743 both describe threads formed by the combination, via twisting, of two threads where one of them can be made adhesive by heat treatment. The heat treatment joins the fibers of the non-thermofusible thread together and improves the properties of the produced articles.
Likewise, the British Pat. No. 1,322,336 and the Luxemburg Pat. No. 66,345 describe the use of binding substances in order to modify the properties of textile materials.
Nevertheless, none of these disclosures provide wrapped threads having a very good resistance against abrasion from the outside as well as inside, and where the distinctive features of the core are practically unchanged by the presence of the outside wrapping thread, the latter being tied to the core by means of a very small quantity of heat sealing substance, where this substance does not modify the general distinctive features of the obtained thread.